Sensitizing photographic media



Nov. 23, 1965 J. E. w VALLE ETAL 3,219,451

SENSITIZING PHOTOGRAPHIC MEDIA Filed Dec. 11, 1962 'FIG.3.

INVENTORS.

JAMES E. LU VALLE ccasuou M. GOLDBERG JOHN s. PACK M W ATTORNEYS UnitedStates Patent O 3,219,451 SENSITIZING PEOTOGRAPHIC MEDIA James E. LuValle, Stony Brook, N.Y., and Gershon i Goldberg, Arlington, and John G.Pack, Reading, Mass, assignors, by mesne assignments, to TechnicalOperations, Incorporated, a corporation of Delaware Filed Dec. 11, 1962,Ser. No. 243,960 24 Claims. (Cl. 96-67) This application is acontinuation-in-part of Serial No. 68,986, filed November 14, 1960, andSerial No. 233,199, filed October 23, 1962, the latter in turn being acontinuation of Serial No. 840,973, filed September 18, 1959, nowabandoned.

This invention relates in general to the field of photographicmaterials, and more particularly to novel sensitized silver halidephotographic materials. Specifically, the present invention is directedto the sensitization of photographically responsive layers of silverhalide, such as are prepared by evaporation of the silver halide from amolten pool, and the condensation of those vapors on an appropriatesubstrate material. The resultant stratum of condensed silver halide isformed of a large number of microcrystals which are supported on thesubstrate primarily by being adhered directly to each other and directlyto the substrate. Such material is therefore binder-free asdistinguished from conventional gelatin type photographic materials; andeven if a retaining surface layer is applied over the binder-freematerial, the silver halide is still substantially binder-free. Thismaterial, as a photographic medium, and a process for preparing same isdescribed in French patent, No. 1,267,623, granted June 12, 1961 toTechnical Operations, Incorporated.

Other photographic media which are now known and in use are generallycharacterized by an emulsion or gelatin in which aggregates ofphotosensitive material are suspended. The use of an emulsion to holdphotosensitive material on a supporting surface has many disadvantages.Among these is the fact that developing agents must penetrate theemulsion to reach the photosensitive material. Another disadvantage isthe fact that there is a limit to the minimum grain size that can beachieved, due in turn to the fact that the aggregates of photosensitivematerial which are suspended in the emulsion cannot individually bereduced beneath a certain size Without losing or suffering diminution oftheir photo graphic properties. Still another is the fact that asubstantial portion of the area of the photographic medium consists ofgelatin, rather than photosensitive material, and this fact coupled withthe minimum limit on grain size places a limitation on the fineness ofdetail that can be recorded. Further, the aggregates themselves are inthe nature of particles of photosensitive material entrapped in globulesof gelatin, so that each aggregate has the chemical characteristics ofthe emulsion as well as its photographic characteristics. Among thecharacteristics of gelatin emulsions are sensitivity to radioactiveenergy, such as gamma rays, and a tendency to pick up moisture, both ofwhich cause fogging of negatives and shorten the storage life ofphotographic media. Further, as is well known, a gelatin, once wet,cannot be quickly dried without taking special measures which are costlyand tend generally to harm the photographic image, and, as is also wellknown, special measures are required to bond a gelatin, which ishydrophilic in nature, to a film base, which is hydrophobic in nature.Another distinct disadvantage of known emulsion-type films is the factthat they can be used only once.

Media of the type disclosed in the aforesaid French patent generallyexhibit native sensitivities, in terms of ASA speed ratings, for examplein the range of 1 l0 3,219,451 Patented Nov. 23, 1965 to l 10- to whitelight with the response greatest in the blue region. For manyphotographic purposes, it is desirable to have media of higher speed, ormedia which exhibit a so-called panchromatic response.

It is, therefore, the principal object of this invention to impartincreased sensitivity to binder-free, microcrystalline, silver halidephotographic media such as those hereinbefore described.

Another object of the present invention is to provide novel processesfor sensitizing such photographic media, and the products of suchprocesses.

Yet another object of the present invention is to provide a number ofnovel sensitizers for such media and techniques for applying same toachieve sensitization.

Other objects of the present invention are to provide sensitization ofsuch media by the treatment of a surface with sensitizing materialapplied from the vapor phase thereof; to provide sensitization of suchmedia by treatment of a surface with sensitizing material applied fromthe liquid state thereof or from solution; to provide such sensitizationby the vacuum deposition of sensitizing material on said surface; and toprovide such sensitization by methods which can be practiced withapparatus similar to that which is used to prepare the binder-treemicrocrystalline, silver-halide photographic media.

Yet other objects of the present invention are to achieve sensitizationof such media through the use of single chemical elements as sensitizingmaterials; and to provide a number of novel sensitized photographicmedia.

A photographic salt, chosen from the group of silver chloride, silverbromide and silver iodide, and combinations of these, can be formed intoa binder-free microcrystalline photographic medium, for example, bybeing evaporated in near vacuum and deposited by condensa tion in amicrocrystalline form directly on a surface of a supporting medium,under controlled conditions of temperature, pressure and time. Thesupporting medium may be the surface of a solid material, such as glass,photographic quality paper, or photographic quality polymeric film.Alternatively, the supporting medium may be coated on the silver halidereceiving surface with a bonding agent, such as a gelatin, a lacquer, ora normally tacky adhesive, in order to cause the evaporated silverhalide to adhere more securely thereto.

The thickness of the resultant layer or stratum of microcrystallinesilver halide photographic material which can be used can likewise vary,but preferably should be a very thin film. Some degree of photographicutility can be obtained with evaporated silver halide strata as thick asabout 3.5 microns; on the other-hand, it has been found that generallythere is a substantial and rapid falloil of photographic properties withthicknesses in excess of an amount around 0.3 micron. It has been foundthat at silver halide stratum thicknesses of around 0.3 micron oneusually obtains maximum photographic properties, i.e., maximum density,speed, and gamma, one or more of which the present invention can enhanceby the sensitization defined hereinafter. Depending upon the exactconditions of temperature and pressure during evaporation andcondensation of the silver halide, and the particular substrate employedto collect the silver halide vapors, the exact thickness at whichmaximum photographic properties is obtained will vary about 0.1 0.3micron thickness. However, the fall-oil of photographic response isusually quite rapid to either side of that thickness which provides themaximum response. Accordingly, the preferred range of thickness for theevaporated silver halide stratum, for the purposes of the presentinvention, is around a fraction of a micron, particularly around the 0.3micron value, and most particularly from about 0.1 micron to about 0.5micron.

Thus, there is provided a photographic medium consisting essentially ofa continuous layer of microcrystalline photographic material, which isrelatively grainless, or may be termed superfine grain, as compared withprior photographic materials prepared in suspension in an emulsion. Thisphotographic medium has the advantages, heretofore not available, thatit can be developed more easily by liquid and even gaseous developers,since there is no necessity for the developer to penetrate a gelatinousmatrix to reach the photographic medium itself, that it lends itself toprocesses of image transfer and re-use after such transfer, and that itis practically insensitive to ionizing nuclear radiation.

Such photographic media may be made of a single one of theabove-mentioned halides, or of two (or more) of them. In the latter casestarting quantities of each desired halide are vacuum evaporated, in thesame location or separate locations, their vapors mixed in the lowpressure region if they started in separate locations, and their mixedvapors are condensed on a surface on the supporting medium. Thus,starting with appropriate quantities of silver chloride and silverbromide, a layer of silver chlorobrornide is deposited. Or, startingwith appropriate quantities of silver bromide and silver iodide, a layerof silver bromoiodide is deposited. Like the single halide layer, theselayers are of substantially homogenous microcrystalline form.

We have found that certain materials will enhance the photographicsensitivity of the binder-free microcrystalline silver halide layerprepared as hereinbefore described. An astonishing range of materialshas been found to exist which will provide noticeable effects; many ofthese materials have hitherto never been suspected of being capable ofproviding sensitization to any type of photographic medium. Thesematerials have been found to include, for example, generally elements ofthe periodic table (excluding halogens) which are normally solid, i.e.,under standard conditions of temperature and pressure. The presentinvention is also concerned with surface sensitization achieved byprocesses, and the products thereof, in which diverse chemical compoundsboth organic and inorganic are employed as sensitizers. Theincorporation of such sensitizing materials is accomplished in thepresent invention by several techniques. For instance, sensitizingmaterial in some cases can be applied by evaporation and condensationfrom the vapor phase, as by known vacuum deposition techniques; in otherinstances, by precipitation procedures from solutions; and in stillother instances by immersion in solutions or by coating from solution.

By the term sensitizer, without being limited to any particular theoryof sensitization, it is intended to mean a material which, when appliedto the microcrystalline binder-free layer of the photosensitive salt,will enhance the inherent sensitivity thereof over a predeterminedspectral range, hence includes both chemical and optical sensitizers ofthe salt.

According to one aspect of the invention, a particulate, i.e.microcrystalline, binder-free silver halide photographic medium issensitized by the treatment of the surface of a binder-free stratum byone or more sensitizing materials applied from the vapor phase, thedeposition of the sensitizing material being accomplished substantiallyin vacuo and controlled to limit the amount of sensitizing materialdeposited.

Specifically, a binder-free silver halide photographic medium of thetype described is sensitized by the deposition, e.g. from the vaporphase, onto its surface of one or more chemical elements. The depositionof the sensitizing element is controlled to limit the amount of anysensitizing element deposited to a concentration not greater thansubstantially atoms per square centimeter of surface of the photographicmedium being sensitized to achieve media which are normally exposeableand developable into negative image bearing media.

We have discovered also that in some cases a concen' tration between thelimits of 10 and 10 atoms per square centimeter of the silver halidesurface of the media; provides a positive type photographic medium.

Concentration of the sensitizing deposit is controlledl in vapordeposition according to the invention by control of the pressure,temperatures of evaporation and con densation of the sensitizingelement, and the time allowed"; for condensation or deposition of thesensitizing element. The resulting photosensitive medium may beuntreated, or additionally chemically treated, as is hereinafterparticularly set forth, to control the quality of the final sensitizedproduct.

According to one aspect of the invention, the aforesaid medium issensitized by treatment of the surface thereof by one or moresensitizing materials applied from a liquid phase or from solution.

In an important embodiment, the invention provides a photographic mediumcomprising a substrate, such as a sheet-like support of, for instance,photographicallyf inert material, having at least on one surfacethereof,- with or without intervening binding strata, a binder-freemicrocrystalline layer of silver halide, the latter in turn beingtreated with a sensitizing material.

Other and further objects and features of the invention will becomeapparent from the following description of certain embodiments thereofand of methods and apparatus for preparing them. This descriptionrefers, for purposes of illustration, to the accompanying drawings,wherein:

FIG. 1 is a top view of a portion of a known vacuum evaporation machinewhich is useful in practicing the method of the invention;

FIG. 2 is a schematic side view of a portion of such a machine; and

FIG. 3 is a schematic cross-section of a sensitized medium of theinvention.

FIG. 1 shows the table 11 of an existing machine for the vacuumdeposition of metals and similar materials and which is employed in theinvention not only to form the binder-free microcrystalline medium, but,in some cases, to apply the sensitizing material to the medium. A basicmachine of the kind referred to is illustrated and described in the bookVacuum Deposition of Thin Films, by L. Holland, published by John Wileyand Sons, Inc, New York city, 1948, pages 7 and 8. A Vacuum coating;machine model LCI-14A of the Consolidated Electr cdynamics Corporationwas used in achieving some of the results mentioned below. This machinehas a belljar (FIG. 2) about 13 inches in diameter and 24 inches inheight on the table 11 under which a low-pressure, near vacuum region isprovided. The location of the bell-jar when in place on the table 11 isindicated by the dashed circle 12. The space under the bell-jar isexhausted through an opening 13 in the table 11.

Electric power terminals 15, 16, 17 and 18, 19, 20 (FIG. 1) are providedon the table 11 for supplying current for melting the silver halidesource material or the sensitizing material, as the case may be, to beevapoprated in vacuum, and a pair of auxiliary terminals 21 and 22(FIG. 1) supply operating voltage (e.g. volts, A.C.) for auxiliarydevices. These terminals are all within the locus 12 of the rim of thebell jar. A first electrically conductive container, boat or filament,24,. which may be made of molybdenum, tantalum or tung-- sten, forexample, is connected by two stiff electrical conductors 25 and 26 to apair of the power terminals. 15 and 18, respectively. The conductors 25and 26 also support the open boat or filament 24 in a fixed positionabove the table 11. Bolts 15.1 and 18.1 (FIG. 2) fasten the free ends ofthese conductors to the two power ter-. minals 15 and 18, which areusually threaded for that purpose. The starting material (not shown) tobe vacuum evaporated is placed in the open boat or fila ment 24.

When it is desired to vacuum evaporate two quantities of startingmaterial in separate locations, a second boat or filament 31 can beemployed, supported on two con ductors 32 and 33, as is shown in FIG. 1.These conductors may be connected to two separate power terminals 16 and19, respectively, as shown in FIG. i, or if desired they may beconnected to the same power terminals 15 and 18 as the first filament24. With two filaments connected to separate pairs of terminals as inFIG. 1, it is possible to control the current to each filamentindependently. Obviously, a third filament (not shown) can be added,connected to a third pair of power terminals 17 and 20, if desired.

In operation, a body or substrate 45 (FIG. 2), to be coated with thecondensate from the vapor of a material (not shown) vacuum evaporatedfrom the filament or boat 24, is supported by any suitable means (notshown) within the bell jar 14 above the filament 24 at a suitabledistance therefrom. Where it is desired to form the binder-freemicrocrystalline silver halide medium, the starting material is at leastone silver halide, chosen from the group of silver chloride, silverbromide and silver iodide. If only one of these compounds is to becoated on a surface on the body 45 a single filament 24 will sufiice. Iftwo of these compounds are to be coated simultaneously on the body 45,for example, silver chloride and silver bromide, or silver bromide andsilver iodide, a quantity of each compound may be placed on the singlefilament 24, or two filaments 24 and 31, as in FIG. 1, may be employedand a quantity of each compound may be placed separately on eachfilament. Where it is desired to sensitize the medium by evaporation, aquantity of sensitizer is placed on filament 24 and the medium is thenused as body 45. In both cases the region under the bell jar 14 isevacuated to a low pressure, preferably in the range of about to aboutl0 millimeters of mercury, although pressures within wider limits, from0.1 millimeter of mercury to less than 10* millimeters of mercury can beused. It is preferred to evacuate the region under the bell jar to theworking pressure prior to applying heating current to the filament 24(and filament 31, if used), so that the elevated conditions oftemperature are not prolonged.

The body 45, which is the target for the vapors of the startingmaterial, is spaced from the filament 24 (and filament 31, if used) adistance such that condensation of the vapors occurs at a condensationtemperature above room temperature, preferably in the range of 30 C. to50 C. At a pressure in the range of 10 to l0 millimeters of mercury, thetemperature in the region above the filament 24 is substantially in thisrange at a distance about 3 /2 inches from the filament, as measured bya copper-constantan thermocouple. Under these conditions, the process iscarried on for a period of time, about one minute or less to one-halfhour, depending upon the temperature and pressure conditions selected,until the starting material has been deposited on the target body 45 toa desired thickness.

It is preferred that the temperature of the silver halide pool and thepressure of the system be substantially stable during the silver halidecoating operation: for example, the temperature may be at about 560 C.and the pressure at about '10- mm. Hg when evaporating sil ver bromide.To attain stable values before coating of the substrate body 45 begins,a mask (not shown) may be interposed between the boat and the substrate,and after the desired temperature and pressure are obtained andstabilized, the mask would be removed and coating of the substrate wouldbe commenced. After a desired thickness of coating is obtained, saidmask may again be interposed to stop the substrate coating operationWhile the silver halide pool is cooled and the vacuum broken.

When forming the unsensitized medium, the substrate body 45, as shown inFIG. 2, may be a sheet of glass or alternatively, it may be a sheet ofpaper, plastic film, or

other conventional and suitable photographic quality substrate material.The silver halide starting material evaporated from the filament 24 inFIG. 2 condenses on a surface of the substrate sheet as amicrocrystalline coating or layer. As the silver halide vapors condenseon this surface, small crystal particles form and coalesce to form atightly-packed layer wherein the crystals are sup ported on thesubstrate by being adhered directly to each other and to the substratewithout the need of a binder. The density of a layer formed in thismanner, has been measured as follows:

Using a body 45 masked by a shield having an aperture which was a square5.7 cm. on each side, a layer of silver bromide was deposited on asurface on the body through the aperture to a mean thickness of 2.2microns as measured by a spectrophotometer using the method of opticalpath ditferences between reflections of controlled light from the frontand back surfaces of the layer. In this example, the thickness of thepolycrystalline layer of silver bromide varied from 1.94 microns at theedge to 2.24 microns at the center. The body 45 was weighted before andafter coating to obtain the weight of the layer. The volume of the layerwas calculated from the dimensions of the aperture and the meanthickness, and found to be:

The weight of the silver bromide layer was found to be 0.44 gram. Fromthese values, the density of the silver bromide layer was calculated tobe 6.16 grams/ cc. The density of solid silver bromide crystals is 6.47grams/cc. as given in the Handbook of Chemistry and Physics, 14thEdition, page 265. The ratio of the densities of this polycrystallinelayer to solid crystals is therefore This indicates that the layer 46 isvery tightly packed and has a density closely comparable to that of thesolid crystal of the starting material.

The polycrystalline layer of silver halide can be deposited also on abonding type of substrate, as suggested above. The supporting body, forexample, can be a film made of a cellulose derivative or other polymers.This film has on one surface a subbing stratum of soft material, such asa layer of shellac or a water-permeable colloid, for example, gelatin.The evaporated layer of silver halide is deposited on the subbingstratum. Due to the softness of the subbing stratum, the first crystalparticles of the silver halide which are deposited on it penetratesomewhat, and the coalescense of subsequent particles of the silverhalide on the initial particles serves to bind the silver halide crystallayer to the supporting body somewhat more securely than had the subbingstratum not been employed. Obviously, a glass body can be used in placeof the synthetic resin body if desired.

If it is desired to fix an image on a sample of the originalphotographic medium, the use of a layer 46 sufiiciently thin to resultin development of the image through the entire thickness of the layerwill prevent re moval of the image when the remaining silver halide isdissolved in the fixing bath. Otherwise, upon dissolution of theunderlying silver halide, the silver image floats 01?. Alternatively, aliquid pervious retaining sheet can be first applied to retain thedeveloped image, and then dissolution of silver halide in the fixer willnot cause loss of the developed silver particles. Rather than em ploysuch expedients as this, it is preferred to use silver halide stratawhich are sufficiently thin to result in development of light struckareas down to the supporting substrate, whether or not surfaceprotective layers or sheets are employed. Since the crystal structureresulting from the present process of evaporating silver halide providesa continuity of contact between grains both laterally across the face ofthe photographic material as well as downwardly through the silverbromide layer to 95.3 percent the substrate support material, thedevelopment process :spreads laterally from a light struck to adjacentgrains :as well as downwardly through the thickness of the layer.Therefore, if the thickness of the silver halide layer is too great,development down to the substrate can result in an intolerable loss ofacutance and image sharpness. It has been found that a silver halidelayer of about 0.3 micron in thickness can be developed down to thesubstrate without appreciable loss of image sharpness and withoutfogging.

In view of the fact that maximum speed, density, and gamma, are allobtained without a 0.3 micron thick layer of silver halide, and sincethe ability to develope down to the substrate without noticeable loss ofimage sharpness or fogging is likewise obtained at this thickness ofaround 0.3 micron, it is apparent that this thickness provides theapproximate optimum for the sensitized photographic material of thepresent invention. These factors however are not intended to excludeentirely slightly thicker layers of silver halide, of say up to about3.5 microns, from the scope of this invention, since such layers can beused where the maximum properties are not essential or desired and otherconsiderations outweigh the loss of photographic properties suffered,such as are suggested in the aforesaid French patent.

As materials which can be evaporated onto a surface to providesensitization of the microcrystalline binder-free silver halide arenormally (i.e. under standard conditions of temperature and pressure)solid elements other than halogens, selected from the group of elementsof the periodic table classified in Groups I through VI and VIII.Specific examples of chemical elements which we have vapor deposited onthe outer surface of a microcrystalline, binder-free silver halidephotographic medium to of coating level or concentration is set forth intwo columns entitled respectively Normal and Solarized and a column alsohas been included entitled Fogged. Where all three, or two of three, ofthe above can be achieved, fogging is obtained with the thickest (orthicker of the two) coatings of the elemnt involved. Inasmuch as foggingis undesirable, detracting from the photographic qualities of images,conditions wherein fog occurs should be avoided generally. Where normaland solarized images are obtained with a given element, the thickerlayer, i.e. the heaviest concentration, yields the solarized image. Ingeneral, where a normal image is obtained, the layer of sensitizermaterial is not substantially greater than 10 atoms per squarecentimeter of adjacent surface of the photographic silver halide. Layersin heavier concentration yield either solarized images or fogging.

The last three columns set forth the approximate pressure in millimetersof mercury, time used for achieving appropriate deposition of thesensitizer vapor, and either the voltage or current through a filament,at which voltage or current, satisfactory vapor deposition of theelement is obtained. The filament used in most cases in Table I istungsten and has approximate dimensions of 0.75 x 2.215 x 0.002 inches.In some cases, a tantalum filament or other filament material ispreferably employed to avoid having a filament with which the startingmaterial reacts chemically. For instance, for vapor depositing antimonyand bismuth a tantalum filament is preferred. The teachings of Hollandat pages 110-114 in his aforesaid book can be followed in many cases,particularly in the use of a boat form of filament.

To obtain the results set forth in Table I starting quantities of 10milligrams or less of each element are employed) TABLE I Resultsobtained as function of coating level Evaporation conditions for normalimage Normal image solarized image Pressure Volts or Fogged amps Time(sec) 73 amps. 3 amps. amps. 90 amps. 2 amps. 25 amps. 43 amps. volts.55 volts. 70 amps. volts. 135 volts. 180 amps. 75 volts. 15 volts.volts. 18 amps. 2.2 volts. 40 volts. 40 volts. 25 amps. 56 volts. amps.amps.

N 4 4 4NNNNNNNNNMNNNNNNNNNNNNMNNNNNNN 44 amps.

increase the photographic sensitivity thereof and with which, in eachcase, there can be obtained upon standard exposure and development anormal (i.e. a negative) image, a solarized (i.e. direct positive) imageor both, are set forth in tabular form in Table I following. In this Themedia sensitized to provide normal images, upon exposures of relativelyshort duration, for example second, and subsequent development will ofcourse yield negative images. However, some of these media, if exposedinstead for relatively long periods, for example 30 table, the type ofimage ultimately achieved as a function 75 seconds, will exhibit atendency to solarize. This solarization tendency can be inhibited bytreatment, as by immersion, in a solution of milligrams of ammoniumchloroiridite per liter of water and subsequent drying before exposure.

Deposition of elemental materials can also be achieved from solution.This of particular value in such cases as the use of sulphur andselenium because these latter are diflicult to control in a vapordeposition process owing to their relatively high vapor pressures atrelatively low temperatures. A layer of sulphur, for instance can bedeposited from solution using a colloidal suspension of sulphur indioxane, a quick evaporation vehicle identified in the Merck Index 7thedition, page 387, published 1960 by Merck & Co., Inc. of New Jersey.Selenium and sulphur can be deposited, each from a solution in dimethylsulfoxide (Merck Index) ibid page 373. In each latter case a saturatedsolution is employed at room temperature, and the precipitant is washedwith water with which dimethyl sulfoxide is miscible and in which theprecipitant is relatively insoluble.

Such reactions as may take place at the silver halide surface in contactwith elements of widely varying properties (e.g., sodium, gold,selenium) were not expected to be the same, and as Table I indicates,the conditions for achieving a sensitized medium which will yield anormal image do indeed vary considerably from one element to the next.In certain cases, such as that of sodium, which is difiicult to workwith because it tends to react with moisture and sputters when heated,greater precision of control of conditions is necessary to achievedesired images. Our investigation of the thirty-five elements mentionedabove indicates, however, that any element, with the exception of GroupVII A, the inert gases, the halogens, nitrogen, hydrogen and possiblyoxygen, which can be handled in a vapor deposition apparatus can bedeposited on the surface of a binder-free silver bromide photographicmedium and can be expected to enhance the sensitivity thereof.

The foregoing methods of the invention can be used with many forms ofbinder-free silver halide photographic medium. One embodiment is shownin FIG. 3 wherein is shown a binder-free, microcrystalline silver-halidelayer 51.20 held on a base 51.22 by, for example, subbing layer 51.21.On the top or outer surface of this layer (as seen in the figure) thereis a layer 52 of sensitizing material. This layer 52 is illustratedexaggerated in size. The layer is, however, thinner than the drawingindicates, being made of approximately 10 atoms per square centimeter ofthe surface of silver halide on which it rests, as is mentioned above.It would be impractical to attempt to illustrate the sensitizing layerto true scale; it should be regarded as an approximately monoatomiclayer. The sensitizer 52 obviously has its principal or primary effecton the photolytic sensitivity of the surface microcrystals in layer51.20 with which the sensitizer material is in contact.

We have made sensitometric measurements, in a sensitometer adapted forexposing light of 5500 K. color temperature through a brightness rangeof 100 to 1, in steps of transmission density changing in increments of0.20, onto binder-free microcrystalline sensitized media according toFIG. 3. This sensitometer used a ZOO-watt tungsten lamp with a CorningNo. 5900 correcting filter as the source of 5500 K. light, a sectorwheel driven at controlled speed as a timing device, and a step wedge(obtained from Eastman Kodak Company, Rochester, New York) having stepsof transmission density varying from 0.05 to 3.05 in increments of 0.20.The speed thus determined of such media sensitized according to theinvention is of the order of ASA 0.10, a tenfold increase. These speedvalues were measured using the surface developer described hereinafter.Higher speed values can be obtained with other developers.

We have made photographs of printed material consisting of blackcharacters on a white background using binder-free photographic mediasensitized according to the invention. Examples of the results obtainedare as follows:

(1) Lead-sensitized medium.Exposed for V5 second at f/4; developed in 10seconds; yielded a normal (negative) image.

(2) Copper-sensitized medium.Exposed for 3& second at f/4; developed in30 seconds; yielded a normal (negative) image.

(3) Gallium-sensitized medium.EXp0sed for /5 second at f/4; developed in30 seconds; yielded a normal (negative) image.

(4) Zinc-sensitized medium.Exposed for /5 second at f/4; developed in 15seconds; yielded a normal (negative) image.

(5) Selenium-sensitized medium.30 seconds in ammonium chloroiriditesolution following vapor deposition of selenium; exposed for second at;f/4; developed in 10 seconds; yielded a solarized (direct positive)image which was the complete reverse of a normal (negative) image.

These photographs were all contact-printed through a transparency, usinga mercury lamp emitting light through a lens system and an adjustablelens stop. With the stop set at f=3.5, the light intensity one foot fromthe lamp was 35 lumens per square foot. The transparency was set againstthe medium, at a distance of one foot from the lamp. The f settingsstated in the foregoing examples were the settings of the lens stop ofthe lens system.

We have obtained comparable results with silver bromide photographicmedia sensitized, by sulphur or selenium, for example, deposited fromsolution or suspension, as described above.

Among the chemical compounds found which may be vapor deposited ontomicrocrystalline binder-free silver halide medium to sensitize thelatter are organic compounds such as dyes selected from those which areevaporatable Without substantial decomposition below approximately 300C. Typical of the cyanine dyes which can be sublimed at reduced pressureare those disclosed in Experiments on the Electronic Mechanism of thePhotoconductivity of Sensitizing Dyes, H. Meier, Phot. Sc. & Eng, vol.6, #4, p. 235 An example of optical sensitization of a microcrystallinebinder-free silver halide medium in this novel manner is as follows:

Example 1 A quantity of 1,1 diethyl-2,2' carbocyanine chloride(pinacyanol) is sublimed at reduced ambient pressure of about l 10 mm.of Hg at a temperature of approximately 200 C. onto a microcrystalline,binder-free silver halide layer lying on a subbed polyethyleneterephthalate sheet to produce a visible dye layer of substantiallyuniform distribution at a concentration of approximately a microgram per70 square mm. of silver halide surface. Exposure of a portion of themedium for 0.1 sec. to a lamp corrected to 5500 K. through a Wratten 25filter and development in an internal developer produces no indicationof red sensitivity. However, after wetting the dye surface of theunexposed portion of the medium with pure water and drying, upon thesame exposure and development, the medium shows a red speed of the orderof ASA 4X10- and a white light speed of the order of IX 10- Thisprocedure is particularly effective to sensitize microcrystallinebinder-free silver halide media with appropriately vaporizable dyes thatare poorly soluble or relatively insoluble in aqueous solution. Theapplication of water in the last step is believed to provide thenecessary aggregation of dye molecules adsorbed on the silver halide.

to the use of these specific compounds.

Obviously, by this method, concentrations of some dyes can be applied tosuch media, which concentration could not be possibly achieved throughapplication from aqueous or alcohol solutions.

Condensation products of alkylene oxides can be employed to increasesensitivity of microcrystalline binderfree silver halide by simplyapplying the material to the surface of the silver halide layer.Alkylene oxide polymers, generally referred to herein as polyglycols,may be formed from monomers which contain 2 to 4 carbon atoms, e.g.ethylene, propylene and butylene oxides, as is well known in the art.Likewise condensation products of alkylene oxide with other oragniccompounds may also be used as sensitizers. Polyglycols of these typeshave been used, either alone or in combination with other sensitizers,as sensitizers with gelatin-type silver'halide emul- SlOIlS.

The'use of alkylene oxide derivatives to sensitize microcrystallinebinder-free silver halide media according to the present invention areillustrated in the following specific example, although the invention isno way limited This example takes the form of a table in which all ofthe compounds were applied in 0.5% aqueous solutions and the medium wasimmersed therein for V2 hour at room temperature. In each case,development was made thereafter with an internal developer following astandard exposure. Unsensitized material used for control in each caseshowed a sensitivity on a sensitometric step wedge of 10 steps.

Example 2 Trade name Chemical name pH Results Amidox L Ethoxylatedamides 8.20 13 steps. Amidox C5.-- .-.do 8.40 D0. Macon 1O Nonyl phenolethylene 6. 45 14 steps.

oxide condensates. Stepanol 153 Ammonium alkyl phenoxy 5.80 13 steps.

polyoxyethylene sulfate. Stepanol TBK Alkoxy polyoxyethylene 4. 70 D0.

ethanol.

All materials shown in the foregoing table were obtained from StepanChemical Company, Chicago, Illinois, and

a the chemical name thereof given is believed to be the most Example 3 Amicrocrystalline binder-free silver halide medium of the type describedwas immersed for two minutes in an 0.1 M triethanolamine solution atroom temperature, subsequently washed in distilled water and shaken dry.The sensitized medium, upon exposure and development in an internaldeveloper, showed an ASA speed of about 0.1. Similarly, individualsolutions of triethanolamine alkylaryl sulfonate and triethanolaminelauryl sulfate (the aforesaid being available under the trade namesrespectively of Ninex and Stepanol WAT and obtained from the StepanChemical Company) also provided comparable sensitization. Amicrocrystalline binder-free silver halide medium of the type describedwas also immersed in an aqueous solution of about-0.1 M of ethylenediamine tetra acetic acid in the sodium salt form. This was found toincrease the film speed by a factor of about 2 also. Variations betweenabout 3 to 11 with respect to the pH of the solution deliberatelyintroduced in the use described above of triethanolamine alkylarylsulfonate as a sensitizer, provided no essential change in thesensitization achieved. While /2 hour appeared to be the optimum timefor treatment of the medium with the polyamines, treatment of the silverhalide surface for as little as 1 minute showed a significantsensitization effect.

Among the organic compounds found to act as sensitizers of the mediaemployed in the present invention are certain organic sulfoxides whichcan be represented by the following general formula:

wherein both R and R are various aliphatic or aromatic groupssubstituted and unsubstituted (e.g. alkyl groups such as methyl, ethyl,propyl, butyl, etc.; aryl groups such as tolyl, phenyl, etc.; andaralkyl groups such as benzyl, fi-phenethyl, etc.; alkylene groups suchas ethenyl propenyl, etc.). The radicals represented by R and R can alsobe substituted by functional groups containing, for instance, sulfur,nitrogen or oxygen such as mercapto, amino, methylamino, hydroxyl,methoxyl, etc., as well as the usual halogens. Use of the above organicsulfoxides is illustrated in the following example:

Example 4 Individual solutions of dimethyl sulfoxide, diethyl sulfoxide,dibenzyl sulfoxide, diphenyl sulfoxide and di-ptolyl sulfoxide wereprepared, each by dissolving 20 grams of pure material in a respectiveliter of ethanol. Another solution of dimethyl sulfoxide was prepared bydissolving 20 grams thereof in a liter of water, the other sulfoxidesbeing too insoluble to prepare such aqueous solutions. Individualsamples of microcrystalline binderfree silver halide media of the typedescribed were immersed each in one of the above solutions for 5 minutesand allowed to dry. Upon exposure of each for 0.1 second, followed bydevelopment in surface developer for 30 seconds, in each instanceeffective sensitization by a factor of at least 2 over unsensitizedcontrol media Was achieved. Similar procedures carried out with diethylsulfite (which can be described as diethoxy sulfoxide) yielded noincrease in sensitivity, indicating that the presence of an oxygenlinkage between the sulfur atom and the radicals R and R was inimical tothe phenomenon. Similarly, upon the use of further oxidation products,i.e. the sulfones, sensitization of this magnitude was not observed.

The microcrystalline binder-free silver halide medium used in theinvention can also be chemically sensitized with dyes as shown in thefollowing:

Example 5 A microcrystalline binder-free medium of the type describedwas first immersed in a 20 mg./l. aqueous solution of Na Au (S O for 30seconds, dried and then immersed in a solution of1,l-diethyl-2,2-cyanine bromide for 5 minutes. The latter solution wasprepared by dissolving 0.1 mg. of the dye in 1 liter of water. Themedium was then shaken dry and exposed in a sensitometer. Upondevelopment in a surface developer, the medium was found to have itssensitivity to white light enhanced by about 1 /2 orders of magnitudeover the control medium similarly sensitized with the gold salt alone.

It is of interest to note that this dye is known as an opticalsensitizer for chloro-bromide emulsions, but surprisingly acted in thisinstance as a chemical sensitizer rather than an optical sensitizer.Exposure of the sensitized medium to light in the absorption band of thedye established that no optical sensitization as such was achieved.

The type of media used in the invention may be also sensitized withcertain organic and well-known reducing agents known as the complexedborane hydrides, as will be seen in the following example:

Example 6 A microcrystalline binder-free medium of the type describedwas immersed in a solution of dimethylamineborane in water for 30 to 60seconds, washed with water and allowed to dry in air. Upon exposure andsurface development, it was found that the medium was sensitized byapproximately an order of magnitude in comparison with a controlledunsensitized medium similarly exposed and developed. Similar resultswere also achieved using comparable solutions of methylamineborane,pyridine borane and sodium borohydride.

It has also been found that a number of inorganic compounds may beapplied in solution to the surface of a microcrystalline binder-freesilver halide medium to chemically sensitize the latter. In someinstances the sensitizing material is quite novel.

For instance, the treatment of substantially binder-freemicrocrystalline silver halide media with copper ions from solution hasresulted in markedly increasing the photographic sensitivity of thesilver halide. That copper ions either in cuprous or cupric form, canact as sensitizers was totally unexpected. Indeed, copper salts added toemulsion before the growth of silver halide grains has been shown toseverely reduce sensitivity according to the article, Effect of MetalIon on the Photographic Emulsion, by Shono, Fukuda and Fukawa in theScientific Publications of the Fuji Photo Film Co., Ltd, 1, 69, 1953. Tosimilar effect is the article by Charriou, Compt. Rend., 19489 (1935).

The unexpected enhancement of photographic sensitivity of evaporatedfilm by copper ions is illustrated in the following examples:

Example 7 A aqueous solution of cupric chloride was prepared. Iustbefore use, 1 ml. of this solution was diluted to 50 ml. with water. Amicrocrystalline medium of the type described was immersed in the dilutecupric chloride solution for two minutes and shaken dry. The treatedfilm was exposed in a step-wedge sensitometer to a light sourcecorrected to approximately 5500 K. and developed in an internaldeveloper solution for sec. at 25 C. Sensitometric results indicatedthat an increase in sensitivity by a factor of about 1 /2 overunsensitized control media was achieved.

Example 8 Example 9 An unsensitized microcrystalline, binder-free mediumof the type described was immersed for one minute in the 25% solution ofcupric chloride at room temperature. The adsorbed cupric ion wasconverted to cuprous ion by immersing the medium in a mixed solution of0.1 M sodium bisulfite and 0.1 M sodium bromide for 15 seconds. Uponexposure and development in the same manner as set forth in Example 8,sensitometric results from the developed medium indicated that thephotographic sensitivity thereof had been increased by a factor ofapproximately 2, somewhat more than had been achieved with cupric ionalone. As in Example 8, the sensitivity could be further enhanced iffollowing conversion of the cupric ion to cuprous ion, the medium wasthen immersed for 15 seconds in an 0.5% EDTA solution.

Other inorganic salts in aqueous solution can be employed as sensitizingagents for the media heretofore described as illustrated in thefollowing example:

Example 10 Binder-free silver halide media of the type described wereimmersed in 0.2 M solutions of respectively ammonium bromide andammonium acetate, and then dried. In both cases, following exposure anddevelopment in an internal developer, sensitization by at least a factorof 2 was achieved. Optimum results were obtained by immersion in therespective solutions at 40 C. for 30 minutes, although reasonableresults could be obtained after 5 minutes.

It has also been found that the photographic sensitivity of the silverhalide in microcrystalline media of the type heretofore described can beenhanced with hydroxyl ions provided from inorganic bases. Examples ofsuch sensitization are as follows:

Example 11 A microcrystalline binder-free silver bromide layerevaporated onto a polyethylene terephthalate sheet was immersed at roomtemperature for 30 seconds in an 0.04 N solution of sodium hydroxide andthen dried. Following exposure and development for 30 seconds in asurface developer, this treatment was found to have increased thesensitivity of the medium by a factor of 4 over the photographicsensitivity of an unsensitized control medium.

Example 12 An unsensitized medium similar to that heretofore describedin Example 11 was immersed for 5 minutes in a 4% ammonium hydroxidesolution and then dried, exposed and developed for 30 seconds in asurface developer. The sensitization achieved was approximately the sameas that resulting from treatment with sodium hydroxide.

In all the preceding examples, and in the preparation of theunsensitized evaporated film used therein, the highest purity materialsobtainable were employed to insure that the effects noted were not dueto unknown impurities.

The surface developer which is used in the examples hereinbeforedescribed is prepared and used as follows. Three stock solutions areprepared, preferably using triplydistilled water. These solutions are:

in 250 cc. of water;

Sodium carbonate (anhydr) 78.00 If monohydrate, use 91.26 Potassiumbromide 2.0

in 1 liter of water;

Gelatine plus water to make 250 cc.

Solution (a) decomposes with time, solution (b) keeps indefinitely, andsolution (c) should be kept refrigerated to inhibit decomposition.

These solutions are used in equal proportions to make the developer.They are mixed by adding ml. quantities of, first, solution (b) tosolution (a), and then 20 ml. of solution (c) to the mixtures ofsolutions (a) and (b).

The internal developer used in some of the examples is formed in thesame manner, but to the mixture of (a), (b) and (c), 3 ml. of a 1%sodium thiosulfate solution is then added.

From the foregoing description of the inventiton and the numerousexamples described, it will be appreciated that we have discovered thatthe evaporated binder-free silver halide medium hereinabove describedcan be effectively sensitized for photographic purposes. Since thesilver halide medium of the present invention is dry formed under hightemperature and vacuum evaporation, to form a very densemicrocrystalline stratum, as distinguished from the conventional wetformed gelatine emulsion silver halide media, the two media are notanalogous. Indeed, the examples of this specification show: that somematerials that act as sensitizers for one medium, act as desensitizersfor the other; that some materials that act as dye sensitizers for onemedium, act as chemical sensitizers for the other; and that somematerials that do not act or are unknown as sensitizers for the gelatinetypes medium shown herein to be sensitizers for the evaporatedbinder-free medium. From the foregoing it will also be apparent that ourinvention is particularly concerned with the sensitization of very thinlayers of evaporated binder-free silver halide material, i.e., layershaving a thickness of from about 0.1 to about 0.5 micron in thickness.

Since certain changes may be made in the above product and processwithout departing from the scope of the invention herein involved it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted in an illustrative and notin a limiting sense.

What is claimed is:

1. An image recording medium comprising a substrate element having asurface providing a recording area, a photographic layer of vapordeposited photosensitive silver halide microcrystals in substantiallycontinuous phase supported upon said element and substantially coveringthe extent of said area, said layer being adhered directly to saidsubstrate and said microcrystals being cohered directly to each other,said layer having a density less than that of said halide in solidcrystalline form, said layer being a fraction of a micron in thickness,and a surface portion of said layer over said area having been treatedwith a sensitizing material to provide an increased photographicsensitivity for said surface portion.

2. An image recording medium as set forth in claim 1, the extent of saidarea, said layer being adhered directly to about 0.5 micron.

3. An image recording medium as set forth in claim 1, wherein saidsilver halide is silver bromide.

4. An image recording medium as set forth in claim 1, wherein saidsilver halide comprises a plurality of halides.

5. An image recording medium as set forth in claim 1, 'wherein saiddensity is about 95% of that of said halide :in solid crystalline form.

6. An image recording medium as set forth in claim 1, :and furtherhaving a protective layer of material overlying said stratum and coheredto the surface thereof and sandwiching it between said layer and saidsubstrate.

7. An image recording medium as set forth in claim 1, wherein saidthickness is about 0.3 micron.

8. An image recording medium as set forth in claim 1, wherein saidsurface portion of said layer is that surface portion remote from saidsubstrate element.

9. A silver halide photographic element comprising a substrate sheethaving a surface providing a recording area, and a photoresponsive layerhaving a stratum of substantially binder-free, vapor deposited silverhalide microcrystals supported on said surface of said sheet andsubstantially covering said area of said sheet, said stratum having athickness of a fraction of a micron and a density of less than that ofsaid halide in solid crystalline form, said layer further including aphotosensitizer for said halide applied and distributed substantiallyuniformly over a surface of said stratum over said area.

14). An element as set forth in claim 9, wherein said thickness is fromabout 0.1 to about 0.5 micron.

11. An element as set forth in claim 9, wherein said photosensitizer isa material selected from the group consisting of titanium, silver,aluminum, arsenic, gold, barium, beryllium, bismuth, cadmium, cobalt,chromium, copper, iron, gallium, germanium, indium, manganese,magnesium, sodium, nickel, neodymium, lead, palladium, praseodymium,praseodymium, platinum, antimony, selenium, silicon, tin telluriumthallium vanadium zinc samarium and sulfur.

12. An element as set forth in claim 11 wherein said photosensitizeralso includes a chloroiridite salt.

13. An element as set forth in claim 11, wherein said thickness is fromabout 0.1 to about 0.5 micron.

14. An element as set forth in claim 11, and further having a protectivelayer of material overlying said photoresponsive layer and cohered tothe surface thereof and sandwiching it between said protective layer andsaid substrate sheet.

15. An element as set forth in claim 11, wherein said surface of saidstratum is that surface remote from said substrate sheet.

16. A method of forming a silver halide photographic element, comprisingevaporating silver halide under a high vacuum with said silver halide ata temperature in excess of its melting point, condensing the silverhalide vapors over a surface area of a base member to form a layer oflight responsive silver halide upon said base as a support therefor,said evaporation being conducted from a pool of molten silver halide,said evaporation and condensation being effected under substantiallystable conditions of pressure and temperature to afford substantiallyuniform characteristics to the silver halide deposit, and wherein saidsilver halide is deposited to a thickness sufficient to coversubstantially said entire area of said base member but no greater than afraction of a micron, and applying a silver halide photosensitizer tothe surface of said silver halide layer.

17. A method as set forth in claim 16, wherein said thickness is betweenabout 0.1 and about 0.5 micron.

18. A method as set forth in claim 16, wherein said photosensitizer isapplied by vapor deposition thereof onto said silver halide surface.

19. A method as set forth in claim 18, said vapor deposition is effectedunder high vacuum.

20. A method as set forth in claim 16, wherein said photosensitizer isapplied by immersing said layer in a liquid medium containing saidphotosensitizer.

21. A silver halide photographic element comprising a substrate element,a photoresponsive layer having a stratum of substantially binder-free,vapor deposited silver halide microcrystals supported by said elementand substantially covering an image recording surface area thereof, saidstratum having a density less than that of said halide in solidcrystalline form, a surface portion of said stratum over said areahaving been treated with a sensitizing material to provide a photolyticsensitivity greater than that of the adjacent portion of said stratumand a protective layer of material overlying said photoresponsive layerand cohered to the surface thereof and sandwiching it between saidprotective layer and said substrate element.

22. A photographic element as set forth in claim 21,

1 7 wherein said surface portion of said stratum is that surface portionremote from said substrate.

23. A photographic element as set forth in claim 21, wherein saidsurface portion of said stratum has a photosensitizer for said halideapplied and distributed substantially uniformly thereover.

24. A photographic element as set forth in claim 23, wherein saidsurface portion of said stratum is that surface portion remote from saidsubstrate.

6/1961 France. 9/1958 Great Britain.

18 OTHER REFERENCES Evans et al.: Journal of Photographic Science, vol.3, pages 73-87 (1955).

Nail et 211.: Physical Review, vol. 98, page 1557 (1955).

Nelson: Journal of Optical Soc. of America, vol. 46, pp. 1016-9 (1956).

Moser et 211.: Physical Review, vol. 102, pp. 1519-23 (1956).

Yamada et al.: Chemical Abstracts, vol. 50, pages 11147-8 (1956).

NORMAN G. TORCHIN, Primary Examiner.

1. AN IMAGE RECORDING MEDIUM COMPRISING A SUBSTRATE ELEMENT HAVING A SURFACE PROVIDING A RECORDING AREA, A PHOTOGRAPHIC LAYER OF VAPOR DEPOSITED PHOTOSENSITIVE SILVER HALIDE MICROCRYSTALS IN SUBSTANTIALLY CONTINUOUS PHASE SUPPORTED UPON SAID ELEMENT AND SUBSTANTIALLY COVERING THE EXTENT OF SAID AREA, SAID LAYER BEING ADHERED DIRECTLY TO SAID SUBSTRATE AND SAID MICROCRYSTALS BEING COHERED DIRECTLY TO EACH OTHER, SAID LAYER HAVING A DENSITY LESS THAN THAT OF SAID HALIDE IN SOLID CRYSTALLINE FORM, SAID LAYER BEING A FRACTION OF A MICRON IN THICKNESS, AND A SURFACE PORTION OF SAID LAYER OVER SAID AREA HAVING BEEN TREATED WITH A SENSITIZING MATERIAL TO PROVIDE AN INCREASED PHOTOGRAPHIC SENSITIVITY FOR SAID SURFACE PORTION. 